64 THE VOYAGE OF H.M.S. CHALLENGER, 



produced to a sharp point ; the antero-lateral angle of the carapace also terminates in a 

 pointed process, curved upwards and forwards, the posterior margin of which is perfectly 

 smooth. The anterior angle or tooth of the lateral branchial margin is large, and extends 

 to a level with the antero-lateral angle of the carapace. Those posterior to it decrease in 

 size gradually, until they become at the eighth reduced to a rudimentary condition. 



The pleon, with the exception of the first somite, which is the narrowest, gradually 

 dimiuishes in width posteriorly. This is due chiefly to the relative size of the coxal 

 plate which is appended to each somite. Each is produced laterally to a point ; in each 

 succeeding somite .the postero-lateral margin becomes more prominent, and in the fifth 

 bears a second angle or point. There is a small central tooth on the posterior margin 

 in the median line of the fifth somite, and a crenated edge along the posterior margin of 

 the sixth. 



The animal is extensively covered with a thick fur, longest on the second pair of antennas 

 and along the anterior edge of the several teeth on the lateral margin of the carapace. 

 On the dorsal surface of the carapace, as well as on the pleon, the surface is smooth, the 

 hairs apparently having been rubbed off by friction. Examination of the surface that 

 has been protected shows that the fur partakes more of a pilose than of a hairy nature. 

 The posterior pair of pereiopoda has the dactylos in the male flat, lanceolate, and fringed 

 with small hairs ; and it articulates at a right angle with the narrowest axis of the propodos. 

 In the female the dactylos is shorter and more robust than in the male, and carries 

 on the middle of the inner side near the base an elevated oval ridge fringed with a regular 

 series of fine spines corresponding with a stout pollex, about two-thirds of the length of 

 the dactylos, and similarly armed with minute hair-like spines. 



The ova were numerous, of a yellow colour, but none of them sufficiently developed 

 to show the character of the brephalos. 



Observations. — The general aspect of the animal agrees with that of Ibaccus incisus, 

 (Perron) {Ibaccus peronii), as given by Leach, 1 which differs slightly from the figure given 

 by Desmarest, 2 and in the description of the armature as given by Milne-Edwards. 3 

 In Leach's figure there are six teeth represented on the lateral branchial margin of the 

 carapace, posterior to the antebrachial cleft. Desmarest says there are five, and his 

 figure shows that the number includes the anterior branchial angle, but not the anterior 

 angle of the carapace in advance of the branchial cleft. Milne-Edwards agrees with Leach 

 in his description : — " Bords lateraux de la carapace tres oblicpies et amies de septs dents, 

 clont une seule situee au devant de la grande, echancrure laterale, et formant Tangle 

 anterieure." We might be inclined to consider our species as being only a variety of 

 Ibaccus incisus, but for one or two differences of importance. The chief of these is found 

 in the formation of the second (homologically the third) joint of the second pair of antennas, 



1 Zool. Miscell, vol. ii. p. 152, pi. exix. 2 Consid. des Crust., p. 183, pi. xxi. fig. 2. 



3 Nat. Hist, des Crustaces, t. ii. p. 287. 



